Transglucosidase (also known as 1,4-alpha-D-glucan-6-alpha-D-glucosyltranferase and as transglucosylase) has been obtained from various microorganisms. It is an enzyme which causes the formation of the trisaccharide panose and the disaccharide isomaltose from maltose by bond cleavage and bond formation. These oligosaccharides are non-fermentable and thus find application in the food, soft drink and sake industries, as well as in the formulation of new foods. See, for instance, Nunokawa et al, Japanese Pat. No. Sho 56(1981)-27236. They describe a method for producing transglucosidase and glucoamylase by culturing a strain of Aspergillus saitoi or A. usami. The culture filtrate is passed through a resin-containing column which retains the transglucosidase while the glucoamylase passes in the effluent. The transglucoside is removed from the resin with an acetate buffer solution at pH 5.5. Also, Pazur et al in "The Isolation and the Mode of Action of a Fungal Transglucosylase", from the Department of Biochemistry and Nutrition, University of Nebraska, Lincoln, Neb., Archives of Biochemistry and Biophysics, Volume 93, pages 43-49 (1961) describe a method for obtaining the transglucosylase of Aspergillus niger that involves separating this enzyme from the other co-produced carbohydrases by chromotography and adsorption on DEAE-cellulose (diethylaminoethyl-cellulose), starch, and carboxymethylcellulose.
On the other hand, Tamura et al in U.S. Pat. No. 4,247,637 describe a process for the production of thermostable glucoamaylase from a strain of Talaromyces duponti, which involves culturing the strain in a nutrient medium and isolating the enzyme. After they culture the strain and remove the mycelia by filtration, they pass the filtrate through active clay and find the glucoamaylase in the effluent. There is no recognition whatsoever by Tamura et al that Talaromyces duponti will also secrete transglucosidase, let alone a very thermostable transglucosidase.
Accordingly, it has been discovered by the present inventors that thermostable transglucosidase can be prepared by culturing cells of Talaromyces duponti in a suitable nutrient medium.